1. Field of the Invention
This invention relates generally to vehicle axles, and more particularly, to a composite tubular vehicle axle having each of its opposite ends encased within a tubular metal sheath.
2. Description of the Related Art
This invention is directed to the providing of a metal-sheathed composite axle for use with vehicles. In the manufacture of vehicles, an axle is typically utilized to support the weight of the vehicle, as well as the transferring of the torsional loads of braking and acceleration from the drive train to the wheels of the vehicle, with the wheels being mechanically mounted to the axle in ways well known in the art.
Axles traditionally have been made of metal due to metal's strength; however, metal axles are not without some drawbacks. For example, when used in go karts and midget go karts, a metal axle can be bent by sustaining an impact at its end if the side of the kart crashes into the wall surrounding the track or if the vehicle is struck in the vicinity of its axle by another vehicle.
Thus for example, one of the standard chrome-moly steel axles used in connection with the aforesaid vehicles is made to bend when it is subjected to 1161 pounds. Furthermore, once the axle is bent, the vehicle needs to be taken out of service and repaired, since the bent axle is permanently bent.
Attempts at strengthening axles have often focused on the dimensions associated with the axle, the selection of the metal from which the axle is fabricated, or the formulation of the alloy used in its manufacture. Whatever option is selected, weight is a consideration whether it relates to the mileage the vehicle gets or the speed of the vehicle: when it comes to weight and either mileage or speed, lighter typically translates as better. However, regardless of which option is selected, if the axle sustains a significant blow to its end, the axle may become bent.
The aforesaid options have been the ones that typically have received attention from axle designers because of prior problems using composites in connection with axles. Composite materials (graphite, boron, aramid, or glass fibers held in epoxy, polyester, vinylester matrices etc.), have extremely high strength to weight ratios. Thus, tubular shafts made of a composite material are typically lighter in weight than comparable metal shafts or rods, plus they are capable of high stiffness-to-weight-ratios. Consequently all-composite shafts have started to replace metal shafts for the transmission of tensile, compression, bending, and/or torsional loads.
Some common applications of all-composite material tubular shafts are rollers in paper mills, bicycle frames, driveshafts, and golf club shafts. In connection with these applications, it is well known in the art of composite shaft construction, to bond end pieces usually made of metal into the open ends of these all-composite tubes to transmit forces into the tube from the adjacent mechanism or structure.
However, the use of composite tubing or composite shafts as a vehicle axle has faced two main problems. First, most vehicle axles have multiple load locations along the exterior of the axle that must transfer torsional loads (drivetrain, braking, wheels) and bending loads (vehicle weight through bearing carrier to chassis). These multiple load locations along the entire length of the axle rule out common or typical composite shafts with end pieces bonded in the ends of the tube as described above. Secondly, to accommodate these multiple load locations along the surface of an all-composite tube, keyway cuts or other mechanical configurations such as key slots would be necessary to connect brake rotors, drive sprockets, and wheels for the transmission of torsional loads. These required mechanical configurations in an all-composite tube would expose the fundamental weakness of all composite materials, namely that although composite lamini have the highest unidirectional properties, they also have very poor bearing stress strengths and interlaminar shear strengths. This is why composites have not found favor in vehicle axles.
For example, if a keyway cut is made in the mid-section of a specially designed all-composite tube for supposed use as a vehicle axle, within a short period of time, the key slot becomes what is known as “mushroomed.” This condition is indicative of the fact that the ultimate bearing strength of the composite material has been exceeded. Alternatively, if a spline cut is made on an axle manufactured as an all-composite tube to transmit normal torsional loads, the splines would quickly shear off indicating that the interlaminar shear strength had been exceeded.
It is thus apparent that the need exists for an axle that utilizes composite technology to result in a light, yet strong axle, and which is relatively easy and cost effective to fabricate and utilize.